The invention relates to a pencil sharpener having a clamping chuck for clamping in a pencil to be sharpened coaxial to a clamping chuck axis by means of radially extending positioning tongues, which clamping chuck is positioned inside a clamping chuck housing, wherein the positioning tongues of the clamping chuck can be released jointly from the pencil through a pivoting movement counter to a spring pressure. The use of the word xe2x80x9cpencilxe2x80x9d as a tool to be clamped in by the clamping chuck of the pencil sharpener in this case refers not only to pencils or colored pencils, but also to cosmetic pencils, leads or similar pencil-shaped articles.
With pencil sharpeners of this type, which are known from German Unexamined Application 2 015 683 as well as U.S. Pat. No. 3,227,140, the pencil is held rotationally fixed in the clamping chuck while the milling devices are driven so as to rotate around the pencil tip. The rotational drive is either motorized or manual. For this, the clamping chuck is guided such that it can move in an axial direction inside an axially displaceable clamping chuck housing, on the machine housing that contains the milling devices. The clamping chuck housing is admitted in the process with spring tension, effective in axial direction toward the milling devices, such that the pencil tip is fed automatically in axial direction to the rotational plane of the rotating milling devices.
With known pencil sharpeners, the clamping chuck has a multi-part design and is therefore expensive to produce. The positioning tongues are positioned individually such that they can pivot around axes that are permanently attached to the clamping chuck housing. The outer actuation ends are operationally connected to a separate holding frame that encircles the clamping chuck axis in the manner of a ring. This holding frame is positioned such that it can pivot around the clamping chuck axis inside the clamping chuck housing and counter to a torsion spring that is effective in a circumferential direction. By pivoting the holding frame counter to the torsion spring pressure, the holding ends of the positioning tongues open the clamping chuck and the pencil can be removed easily. The fact that the holding frame is admitted in a circumferential direction by the torsion spring causes the holding ends of the positioning tongues to automatically pivot back to the clamping position relative to an inserted pencil or to a closed position near the axis.
A similar clamping chuck for a pencil sharpener is known from German Published Application 1 063 934. However, in place of a torsion spring this patent provides for several helical springs, which extend in circumferential direction and admit the holding frame. Another clamping chuck for a pencil sharpener is known from German Patent 472 725. The clamping chuck in this application is formed by several levers, which are positioned pivoting around axes permanently attached to the housing and extend approximately tangential to a lead-through for the pencil. In the region of the lead-through, each lever is provided with a clamping jaw that projects into the lead-through if the clamping chuck is in the closed position. The levers hereby engage with their outer ends in recesses, provided in a clamping chuck lid that can be pivoted, so that during the turning of the lid, the clamping jaws that are held together by spring force are pulled apart approximately in radial direction. These known clamping chucks again have the disadvantage of a multipart design and are therefore expensive to produce.
It is an object of the invention to simplify the design of a pencil sharpener of the aforementioned type. The effect achieved in prior art with a multipart design, for which the parts can be rotated or moved relative to each other, is achieved according to the invention simply with the holding frame and the positioning tongues, which are attached thereto in such a way that they can neither rotate nor move. A separate torsion spring that is effective in circumferential direction is not required because its effectiveness is replaced by the positioning tongues, which are secured on the holding frame in the manner of unilaterally tensed bar springs and by the fact that these positioning tongues rest against locally fixed stops on the clamping chuck housing.
A one-piece design of the holding frame and positioning tongues according to the invention is particularly advantageous. The use of polyoxymethylene (POM) as material for the one-piece clamping chuck according to the invention ensures a continued elasticity of the positioning tongues over a long period of time.
A preferred arrangement of the pencil sharpener according to the invention has the clamping chuck, in the idle position, inside the pivoting guide of the clamping chuck housing and the positioning tongues are not tensioned. This arrangement permits a particularly easy assembly of the clamping chuck, since it must not be inserted - as is standard practicexe2x80x94under pre-stressing into the clamping chuck housing.
The clamping chuck according to the invention preferably can be handled with one hand.
According to another embodiment of the invention, a large degree of design freedom for the holding frame is permitted without influencing the forming freedom, the spring behavior and the pivoting ability of the positioning tongues. This is particularly advantageous because the positioning tongues are secured on the holding frame and, in particular, are produced as one piece with the holding frame.
The spring characteristic of a positioning tongue can be adjusted easily according to an embodiment of the invention by dimensioning its cross-sectional surface in the individual longitudinal areas of the positioning tongue. In the process, the connecting region between positioning tongue and holding frame, in particular, can be protected against high torsional stress that damages the material.